1. Field of the Invention
This invention relates generally to the field of water soluble coloring materials for drawing, painting, and coloring purposes, such as marker inks and paints. In one particular aspect, the invention relates to marking instruments containing liquid inks, and it more specifically relates to the formulation of inks for use in marking pens or, simply, markers. In one preferred form, the invention relates to improvements in coloring and drawing markers for use by young children.
2. Brief Description of the Prior Art
Children's coloring markers usually contain inks which are aqueous solutions of dyes known in the trade as "acid dyes." The term "acid dyes" is actually somewhat of a misnomer in that it does not describe any particular chemical type of dye, but rather refers to the traditional practice of dyeing fabrics from acidified solutions. Not all acid dyes are suitable for use in marker inks, however, and dyes having good chroma and color intensity and good water-solubility characteristics are typically utilized.
Marker inks ordinarily also include such ingredients as humectants, biocides, and surfactants. Humectants function to improve freeze/thaw stability and to control drying out of the marker tip, while biocides serve the obvious function of preventing spoilage of the ink during the expected shelf life of the marker product. In order to limit a grainy appearance of the ink as it is applied and/or to enhance the flow characteristics of the ink, a small amount of surfactant is ordinarily employed. It is important to note that surfactants, when used at all, are included in very low concentrations in marker inks in order to prevent the phenomenon known as "strike-through," where the ink soaks through the paper to which it is applied instead of remaining on the surface.
It is well known that a major deficiency of children's coloring markers is their propensity to leave enduring stains on both skin and clothing. While permanence is a desirable characteristic of the so-called "permanent" markers, it is one of the most objectionable of properties for coloring instruments used by young children. Accordingly, much effort has been expended over many years by producers of these instruments to reduce or eliminate staining. This is attested to by the rather numerous offerings of so-called "washable" markers, which on close examination, are found to remove very poorly from fabrics that are typically used in children's clothing. Most such markers achieve their limited washability by utilizing dyes which have good fugitivity from fabrics and by utilizing lowered dye concentrations in an effort to minimize skin staining. In all cases, however, these "washable" products leave objectionable stains on the skin. The inks used in such markers therefore lack fugitivity from skin.
In a more recent approach, the tints or dyes used in these "washable" markers are produced by the chemical grafting of a chromophore onto a water soluble polymer, such as polyethylene glycol, in an effort to impart improved fugitivity properties to the chromophore. While this approach is a workable one for enhancing fabric fugitivity, it is relatively expensive.
It is therefore one general object of the invention to provide a method of imparting skin fugitivity to a dye-containing composition.
Another object is to provide a water-soluble dye-containing composition which, in addition to being washable from the skin, is more easily washable from fabrics.
A related object is to provide non-toxic washable dye-containing compositions, such as paints and inks, which are suitable for use by young children who may make marks on themselves and their clothing.
Another related object is to impart skin fugitivity to dye-containing compositions without the necessity for chemical or other alteration of the dyestuff itself.
A further object is to impart skin fugitivity to dye-containing compositions which otherwise have good washability from textiles, but quite limited washability from skin.
These and other objects and advantages of the invention will be apparent to those skilled in this art from the following description of the invention and the appended claims.